IPTC Ext Event is a langAlt property, so make sure you enable that in the view editor Advanced screen.
JSON should look like this:
{ id: "C58pHBqUBI", displayName: "Event", prefix: "Iptc4xmpExt", namespace: "http://iptc.org/std/Iptc4xmpExt/2008-02-29/", propertyName: "Event", type: "Text", dependencies: [], linkToFile: {}, readOnly: false, multiLine: false, altLang: [], altLangDefault: "", altLangEnabled: true, disabled: false, }
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